This invention relates to electromechanical transducers and more particularly to electromechanical transducers comprising microminiature elements and methods for their manufacture. Their principle of operation is the attraction of oppositely charged micro-elements which have been manufactured using high resolution fabrication methods developed for integrated circuit production. This allows the elements to be as small as the order of microns, and it allows the separation between capacitive elements to be of the order of microns. As will be seen, the actuation force is inversely proportional to the square of the separation distance, and it is large enough to be of practical use for the separations of the order of microns.
A number of researchers have recently become active in the field of micro-machining. The most pertinent work for this patent is described in Copending application Ser. No. 07/619,183 filed Nov. 27, 1990 by co-inventor Stephen M. Bobbio and entitled "Microelectromechanical Transducer and Fabrication Method," the disclosure of which is incorporated herein by reference. Described is an electromechanical transducer which features a small separation between plates and which avoids the need for individual discrete wiring to each plate.
The Bobbio transducer is formed of a plurality of electrically conductive strips arranged in an array, with adjacent portions of the strips being maintained in a closely spaced relation by a series of spacers positioned between the adjacent portions of the strips. The spacers have electrically conductive portions to distribute the electrical signal within the transducer, thereby forming an internal distribution network and obviating the need for discrete electrical connections to made to each conductive strip in the transducer. The strips are preferably made of flexible dielectric material having an electrically conductive layer on selected outer surfaces thereof. The dielectric strips and spacers are preferably formed from a common dielectric layer using microelectronic fabrication techniques to thereby greatly simplify fabrication and avoid the need for assembling a myriad of microscopic elements.
The transducer of Bobbio was designed with the following goals in mind. Microelectromechanical transducers must be electrically and mechanically robust, so that they can be fabricated with high manufacturing yields and operated over extended periods of time without breakdown. In particular, because of the large numbers of electrical conductors which must be formed in a microelectromechanical transducer, the transducer should be designed so that electrical shorts do not occur during the manufacturing process and during operation over a normal lifetime. Moreover, the structure must be mechanically robust so that it can withstand the various manufacturing processes which are used to fabricate the structure, and can also withstand operation over an extended operational lifetime. Mechanical robustness is particularly important for microelectromechanical transducers, which by their very nature are required to move during normal operation.
The manufacturing processes for the microelectromechanical transducer should also produce high yields for the device. The manufacture of these transducers should also preferably use processes and materials which have heretofore been widely used in the manufacture of similar devices such as integrated circuits.